An electric traction drive, such as may be used in an electric or hybrid vehicle, requires high voltage utilization to produce torque as efficiently as possible within a constrained volume and weight. For such high voltage utilization, an electric drive system may utilize a pulse width modulation (PWM) inverter that is configured to drive a multiphase AC motor. Motor vehicle applications typically employ a three-phase AC motor.
The synchronous frame current regulator has become the de facto industry standard for controlling the current of three-phase inverter and converter systems, due to its current control capability over a wide frequency range. As the synchronous frame current regulator transforms the measured inverter currents into the synchronous frame, low frequency current error is translated into the synchronous fundamental frequency, which is the same as the inverter output frequency. Therefore, when the output frequency is extremely high, the synchronous frame current regulator is vulnerable to low frequency disturbance, e.g., voltage disturbance due to non-ideal switching of the power devices, beat phenomena between the switching frequency and the fundamental frequency, and current sensor errors. For example, if the output frequency is 1.0 kHz, the DC offset in current is interpreted as a 1.0 kHz current error in the synchronous reference frame. Since this frequency is much higher than the current control bandwidth, this error is not easily removed by the synchronous frame current regulator. As a result, the synchronous frame current regulator can not suppress the subharmonic current due to the low frequency disturbances.
In an electric or hybrid motor vehicle deployment, low frequency subharmonic oscillations in the inverter output may result in low frequency torque components in the AC motor and, in turn, motor speed oscillations and “shuddering” of the vehicle. Moreover, such low frequency oscillations represent losses that result in lower motor efficiency.
Accordingly, it is desirable to have an improved inverter control system and technique that reduces subharmonic components at high operating frequencies. Furthermore, other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.